Exploring the plastic-fed Indian mealworm (Tenebrio molitor) gut bacterial strain (Bacillus subtilis AP-04) – A potential driver of polyethylene degradation

Abstract

Plastic biodegradation by microbes is an environmentally friendly and sustainable approach that has no negative consequences. In this study, mealworms were fed with 9 different diets with expanded polystyrene (EPS) and polyethylene foam (PF), after 28 days of incubation mealworm survival rates were highest at 93.3 % when fed wheat bran alone whereas 83.3 % and 80 % when fed EPS and PF exclusively, indicating their adaptability to different plastics and their ability to thrive in various conditions. Histological examination revealed ingestion of EPS and PF found in the intestine confirming through cell wall disruptions. Ten bacterial isolates (AMI-1 to AMI-10) were obtained from EPS and PF-fed mealworms gut. After 30 days in mineral salt media (MSM) with low-density polyethylene (LDPE), AMI-4 showed higher turbidity and biofilm formation. Out of ten isolates seven bacterial isolates produced lipase, six produced proteases and laccases, and all exhibited positive amylase activity, with the highest zone formation in AMI-4. Morphophysical characteristics and 16S rRNA sequencing identified AMI-4 as Bacillus subtilis AP-04 (OR288581). A higher ATP value (783 ± 84.69), LDPE film Weight loss (36.55 %) and CO₂ evolution (15.8 ± 0.99–22.39 ± 1.40 g/l) and the mechanical changes of LDPE film were confirmed through GSM loss 27.24 % and decrease in tensile strength (9.82 ± 0.61–7.98 ± 0.50 Mpa) by Bacillus subtilis AP-04 was recorded at 60 days of incubation. AFM, FTIR, and SEM analyses confirmed degradation in treated LDPE films compared to controls. This study reveals the potential of gut bacterial strain (Bacillus subtilis AP-04) on LDPE film, indicating their potential for bioremediation of plastic waste on a larger scale.